1. Field of the Invention
The invention relates to a magnetic resonance (MR) device which includes a main field magnet system which generates a steady magnetic field in an examination zone and includes:
a magnetizable upper yoke plate which is arranged above the examination zone, PA1 a magnetizable lower yoke plate which is arranged below the examination zone, PA1 a magnetizable yoke wall which interconnects the two yoke plates and encloses an inner space in conjunction with the yoke plates, PA1 a coil which is arranged between the examination zone and the upper yoke plate, and PA1 a magnetizable pole block which is arranged between the examination zone and the lower yoke plate.
The yoke plates, the yoke wall, the pole block and the coil together constitute the main field magnet system which generates a uniform, steady magnetic field. The yoke plates, the yoke wall and the pole block enclose an inner space and conduct the magnetic flux generated by the coil arranged in said inner space. The yoke plates, the yoke wall and the pole block consist of a magnetizable material, for example iron or steel, and hence offer little magnetic resistance to the magnetic flux.
2. Description of the Related Art
An MR device of the kind set forth is known from DE-A 44 17 940. The superconducting coil therein is arranged on a pole piece disposed between the upper yoke plate and the examination zone. Furthermore, a collimator plate is provided between this pole piece and the examination zone.
During an examination the patient is arranged on a patient table in the air gap between the collimator plate and the pole piece arranged underneath the examination zone. The collimator plate serves to optimize the homogeneity of the steady main magnetic field in the examination zone in which the part of the patient to be imaged is present. Because the collimator plate is situated at a small distance from and above the patient, however, the patient is then accessible only from the sides, for example for treatments performed simultaneously with the MR examination.
Contemporary MR imaging methods enable real-time formation of MR images. This possibility can be used notably for interventional applications, for example to provide the surgeon continuously with current MR images during an operation or to visualize the progress of the treatment continuously and instantaneously during minimal or non-invasive techniques.